A typical train includes one or more locomotives, a plurality of railcars and several trainlines. The trainlines include both pneumatic and electrical lines most of which run from the lead locomotive to the last railcar in the train. One pneumatic mainline is the brake pipe. The brake pipe consists of a series of individual pipe lengths each of which secured to the underside of one railcar. Each pipe length is interconnected to another such pipe length via a flexible coupler situated between each railcar. Usually controlled so as to mimic the pressure contained within a storage tank called the equalizing reservoir, the brake pipe is thus one long continuous pipe that runs from the lead locomotive to the last railcar. The brake pipe supplies the pressurized air that is required by the brake control system to charge the various reservoirs and operate the brake control valves of each railcar in the train.
In a locomotive, the pneumatic trainlines include an actuating pipe, a main reservoir equalizing (MRE) pipe, and an independent application and release (IAR) pipe, in addition to the brake pipe. Within a locomotive consist (i.e., two or more locomotives connected together), the MRE, actuating and IAR pipes of each locomotive connect to the MRE, actuating and IAR pipes of adjacent locomotives. Also known as the No. 20 pipe, or simply the 20 pipe, the IAR pipe supplies the compressed air that may be used to control the delivery of pressurized air to, and thus to operate, the brakes of each locomotive in the train.
The brakes of a train, whether on railcars or locomotives, are applied using brake cylinders and associated components.
During braking, the brake cylinders convert the pressurized air that they receive to mechanical force. From the brake cylinders this force is transmitted by mechanical linkage to the brake shoes. When the brakes are applied, it is the brake shoes that are ultimately used to slow or stop the rotation of the wheels on every vehicle in the train.
A typical locomotive has a brake control system such as any one of the various EPIC.RTM. Brake Equipment Systems produced by the Westinghouse Air Brake Company (WABCO). These brake control systems generally include a cab station unit, a keyboard, a display, a locomotive interface unit, a brake control computer and a pneumatic operating unit. The cab station unit generates various signals including those representing the positions of the automatic and independent brake handles, and conveys commands corresponding thereto to the brake control computer. The keyboard also permits a train operator to access the brake equipment, allowing, for example, the operator to input certain set-up parameters. The display allows the operation of the brake equipment to be monitored. The locomotive interface unit (LIU) connects electrical power and certain trainlines to the brake equipment and provides various signals to the brake control computer. Based on the inputs it receives and the software that dictates its operation, the brake control computer essentially controls the overall operation of the brakes. Shown in FIG. 1, the pneumatic operating unit (POU) controls the pressures in the pneumatic trainlines and in various reservoirs so as to control the brakes according to commands received from its brake control computer.
The POU features a pneumatic laminate to which the brake control computer and various pneumatically and electropneumatically operated devices mount. The design of the laminate allows these components to be removed for repair and maintenance without disturbing the piping or wiring of the locomotive. Through a number of ports and internal passages, the pneumatic laminate interconnects these devices to each other and to branch pipes that carry air from or to the actuating pipe, the MRE pipe, the IAR pipe, the brake pipe, the brake cylinder and/or various storage tanks such as the equalizing reservoir. It is through the ports and internal passages of the pneumatic laminate that these devices communicate fluidly with each other and the pneumatic pipes on the train.
Among the devices mounted to the laminate are the independent application and release (IAR) control portion, the brake cylinder (BC) control portion and the brake pipe (BP) control portion shown in FIG. 1. These operating portions of the POU are primarily controlled by the brake control computer.
Shown in FIG. 2, the IAR control portion features pneumatic logic circuitry along with solenoid operated valves by which the pressure in both the actuating and IAR pipes can be controlled. The BP control portion uses pneumatic logic circuitry and solenoid operated valves by which the pressure in the equalizing reservoir and brake pipe of the train can be controlled. The BP control portion also controls the emergency venting and brake pipe cut-off functions. The BC control portion features pneumatic logic circuitry along with solenoid operated valves by which the pressure in the brake cylinders on the locomotive can be controlled. The BC control portion controls the pressure in the locomotive brake cylinders in response to the commands generated by movement of the two brake handles. These automatic and independent brake demand signals may also be generated by pressure changes in the brake pipe, the IAR pipe, the back-up brake or the penalty brake circuitry.
The cab station unit generally includes a handle unit and a cab control unit. The handle unit houses the two brake handles and related components. The cab control unit essentially has a computer and a cab interface card. From the handle unit the cab control computer receives via the interface card the signals indicative of the positions of the automatic and independent brake handles. Based on these inputs, the cab control computer calculates commands representative of how much, or even if, the braking effort should he reduced. Along with other information, the cab control computer then conveys these commands to the brake control computer.
The automatic brake handle is the device that the train operator can manipulate to direct the brake equipment to apply and release the brakes on each locomotive and each railcar of the train. The level to which the brake equipment reduces or increases pressure within the brake pipe, and thus the amount of braking power exerted by the train brakes, corresponds to the position of the automatic brake handle. The independent brake handle, in contrast, allows the train operator to apply and release the brakes only on the locomotive(s) of the train.
The automatic brake handle can be moved from and in between a release position at one extreme in which brake pipe pressure is maximum and the brakes are completely released to an emergency position at another extreme in which brake pipe pressure is zero and the brakes are fully applied. When the brakes are applied, reduction of the pressure in the brake pipe is generally controlled from the lead locomotive via the BP control portion. The exact amount by which the pressure is reduced depends into which of the application positions the handle is placed. It is this reduction in pressure that signals the brake control valve(s) on each railcar to supply pressurized air from the appropriate reservoir(s) to the brake cylinders to apply the railcar brakes. The automatic brake handle positions thus include release, minimum service, full service, suppression, continuous service and emergency. Between the minimum and full service positions lies the service zone wherein each incremental movement of the handle toward the full service position causes an incremental reduction in brake pipe pressure.
The independent brake handle may be moved from a release position at one extreme to a full apply position at the other extreme and to any point within an application zone between those two extremes. As described in detail below, when the independent brake handle is placed within the release position, the brake control computer commands the IAR control portion to vent completely the air contained within a control reservoir, a loss of pressure that the IAR pipe, via the IAR control portion, attempts to match. The BC control portion pneumaticaliy responds to this loss ill IAR pipe pressure by venting air from the locomotive brake cylinders to release the locomotive brakes.
Conversely, when the independent brake handle is then moved into the application zone, the brake control computer commands the IAR control portion to increase proportionately the pressure within the control reservoir, an increase that the IAR pipe, via the IAR control portion, again attempts to match. The exact amount by which the control reservoir pressure is increased depends on how far into the application zone the handle is placed. For example, when the handle is placed into the full apply position, the brake control computer commands the IAR control portion to increase the control reservoir pressure to a nominal maximum value appropriate to the type of train at issue. Specifically, the IAR control portion fully charges the control reservoir to typically 45 psi (or other appropriate value), a level that the IAR pipe, via the IAR control portion, attempts to match. Though the pressure within the IAR pipe approaches close to that contained within the control reservoir, the IAR pipe cannot achieve it due to the mechanical nature of the IAR control portion. Responding pneumatically to the increase in IAR pipe pressure, the BC control portion directs air from the main reservoir to the brake cylinders to apply the locomotive brakes. The pressure in the IAR pipe and the locomotive brake cylinders thus reduces and increases in proportion to the position of the independent brake handle.
The keyboard allows the train operator to input the various parameters necessary to set-up the brake equipment for operation. Through the keyboard, the train operator can select the mode in which the locomotive brake equipment will be operated. In the LEAD CUT-IN mode, the brake control computer permits the locomotive operator to direct control of the train through both the automatic and the independent brake handles. This gives the operator control over the brakes of both the locomotive(s) and the railcars. In the LEAD CUT-OUT mode, the brake control computer permits the locomotive operator to direct control only through the independent brake handle. This gives the operator control over the brakes of the locomotive(s) only. In the TRAIL mode, both brake handles are rendered inoperable except for the emergency position. In a locomotive consist, the brake equipment of one locomotive operating in the TRAIL mode is essentially subservient to the brake equipment of another locomotive operating in either of the LEAD modes. The operation of the BP control portion is affected by the mode in which the locomotive is operated.
The foregoing background information is provided to assist the reader to understand the invention described and claimed below. Accordingly, any terms used herein are not intended to be limited to any particular narrow interpretation unless specifically stated otherwise in this document.